Things are changing quickly. Prices of PV modules have fallen by more than 50% in the 2010-2013 period (and much more slowly after 2013).
On the other hand, manufacturers are offering an increasing number of PV products for residential uses, with their own built-in battery storage and inverters, and panels that are simply plugged into standard home outlets (see on this systems: Solar Tribune).
Overall Costs, Size and Paybacks
In the US, in the south, a 5 kW installed PV system may cost you $20.000, and be large enough to meet all the electricity needs of modest-sized energy-efficient house.
But in the north, the same photovoltaic system will provide a lower part of the needs of the same house; and the cost may be different. The solar resource potential counts a lot, and varies significantly by climate. And so does the payback period.
More annoying, there are a set of soft or business costs that vary according to local factors: permits, inspections, financing, site preparation and, obviously, inputs such as inverters, wiring or tracking systems, not to talk of the labor costs and the business margins of contractors.
These costs can duplicate or triplicate the final costs of the PV system (see, this report of the Rocky Mountain Institute on the issue: “Achieving Low-Cost Solar PV”, for details).
Obviously, a stand alone PV system, with a backup system, will be significantly more expensive... Battery banks used for power storage (lead-acid batteries) are expensive ($6,000-$12,000/set, or more) and have a relatively short lifespan: 8 or 9 years, after which you will have to invest in new batteries.
Making the investment In a PV system more effective
Regardless of the economics of PV systems, there is a rule that you should keep in mind: basic energy improvements involving lighting, cooling systems, appliances and very high levels of insulation and air sealing are critical for the financial sucess of a residential PV system. They reduce drastically the energy needs and enable smaller and cheaper PV systems.
In other words: you should reduce your electricity consumption as much as possible, before installing a PV system.
You should assess your electricity uses, in order to reduce them by 50% or more. You should invest in conservation measures and basic energy improvements. That enables a much smaller PV system, cheaper and able to meet most or all of your power consumption - a goal that you should also keep in mind. It doesn't make sense otherwise (see on this issue: Before Installing a PV System).